In order to improve the interactivity of mobile interfaces several solutions have been proposed, including the haptic modality and information visualisation. For the latter, zooming proves to be a powerful tool to compensate for the small size of the screen. Thus, in this study, the first result underlines that the subjects don't have any difficulty to make the distinction between a zoom-in and a zoom-out when they handle a haptic zoom through a sensory substitution device. The second result underlines that the subjects do not handle more than 25 levels and this, even if they have the possibility of handling more (100 or 1000). Copyright 2007 ACM.